Wormhole-like mesoporous silica templated by double-chained cationic surfactant

Microporous and Mesoporous Materials 124 (2009) 42–44

Contents lists available at ScienceDirect

Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso

Wormhole-like mesoporous silica templated by double-chained cationic surfactant Yong-Xiang Zhao *, Chun-Guang Gao, Yu-Xia Li, Tie-Ming Zhang School of Chemistry and Chemical Engineering, Shanxi University, 92# Wucheng Road, Taiyuan, Shanxi 030006, China

a r t i c l e

i n f o

Article history: Received 20 January 2006 Received in revised form 17 April 2009 Accepted 21 April 2009 Available online 3 May 2009 Keywords: Dioctadecyldimethylammonium chloride Structure-directing agent Mesoporous silica Wormhole-like Template

a b s t r a c t Wormhole-like mesoporous silica materials were synthesized with dioctadecyldimethylammonium chloride (DODAC) as the template and tetraethylorthosilicate (TEOS) as the precursor. XRD, nitrogen adsorption and TEM were employed to characterize the textures and structures of the materials. The mesoporous silica material has pore size of 3.6 ± 0.3 nm, BET specific surface area of 669.3 ± 50 m2/g, pore volume of 1.1 ± 0.2 cm3/g. Ó 2009 Elsevier Inc. All rights reserved.

1. Introduction In recent years, surfactant-templated synthesis strategies have been successfully applied to the preparation of a variety of mesoporous materials. These mesoporous materials have been used extensively in many fields. The choices of template have very important effects on the structure of mesoporous materials. The famous M41S [1] molecular sieves are synthesized with a singlechained cationic surfactant CnH2n+1Me3Br(n > 6) as the structuredirecting agents. Following the M41S, several other kinds of mesoporous molecular sieves, such as SBA [2], HMS [3], MSU-X [4], are prepared successfully with the same strategies. The templates used are amphiphilic triblock copolymer – PEO, neutral amine – dodecylamine, nonionic copolymer – pluronic P123. In aqueous solution, the assembly of double-chained (C12–C18) cationic surfactant is different from that of a single-chained cationic surfactant. So it is interesting to investigate the material structure directed by double-chained cationic surfactant. As we known, few works has been done to prepare mesoporous silica with double-chained cationic surfactant as a structure-directing agent. Anton L. German et al. [5] reported the use of dioctaldecyldimethylammonium bormid (DODAB) to prepare parachute-like structure polymer hybrids. Also Anton L. German group, using DODAB as template, studied the growth of silica over DODAC vesicles and obtained silica-coated unilamellar surfactant vesicles [6]. Jutta Hotz and Wolfgang Meier [7] obtained hollow-sphere polymer with the template of DODAC. The aforesaid published research work focus on preparing vesicle-like structure materials via the

* Corresponding author. Tel.: +86 351 7018371; fax: +86 351 7011688. E-mail address: [email protected] (Y.-X. Zhao). 1387-1811/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2009.04.026

template action of DODAB and DODAC. This work reports a general strategy to prepare mesoporous silica by using double-chained cationic surfactant as a template. The results showed that the wormhole-like mesoporus materials were obtained successfully under proper conditions. This provides an optional way to get this kind of porous materials, and prove double-chained cationic surfactant is a suitable template for preparing mesoporous materials. 2. Experimental section 2.1. Chemicals Dioctadecyldimethylammonium chloride (DODAC) was obtained from China Research Institute of Daily Chemical Industry (RIDCI), and recrystallized twice from acetone. All the other chemicals are analytical grade reagent used as received. 2.2. Preparation of mesoporous silica A typical procedure was as follows: 0.32 g DODAC was added to 40.43 g of deionized water and sonicated for 30 min at 50 °C, which resulted in a clear solution. The solution was adjusted with NaOH to pH = 12.0 ± 0.3, then 2.08 g TEOS was slowly added drop by drop under stirring, whereupon a white precipitate appeared. The suspension was stirred at 30 °C for 24 h, followed by aging at 80 °C for 4 d. The product was collected by filtration, washed with deionized water and dried in air. The final reactant molar composition was about TEOS:DODAC:H2O = 1:0.05:231. For surfactant removal, the HCl–methanol solvent extraction method was used. Generally, about 0.25 g of the as-synthesized sample was refluxed in 45 ml methanol with 4.2 ml of 37% HCl aqueous solution for 48 h. The

43

Y.-X. Zhao et al. / Microporous and Mesoporous Materials 124 (2009) 42–44

14000

Quantity Adsorbed (cm3/g STP)

40

12000

Intensity

10000 8000 6000 4000

Adsorption Desorption

35 30 25 20 15 10 5 0

2000

0.0

0 2

4

6

8

0.4

Fig. 1. Powder X-ray diffraction pattern.

filtered sample was then carefully washed with methanol and dried in air. FT-IR was used to detect the surfactant removing, that is, there were no peaks between 2800 and 2900 cm 1. 2.3. Characterization Nitrogen adsorption–desorption measurements were carried out on a Sorptomatic 1990 unit (ThermoQuest Italia S.p.A.). The samples were outgassed at 150 °C for about 24 h. The pore distribution was dealt by the BJH method. Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku Rotaqflex diffractometer equipped with a rotating anode and CuKa radiation. Transmission electron microscope (TEM) images were obtained using a JEOL JEM-2010 microscope operating at 200 kV.

0.8

1.0

Fig. 2A. N2 sorption–desorption isotherms of the sample after the template removing.

500

400

300

200

100

0

0

0.2

0.4

0.6

0.8

1

Relative Pressure P/P0

3. Results and discussion

Fig. 2B. N2 sorption–desorption isotherms of the sample before the template removing.

0.10 0.08

dV/dD(cm3/g/nm)

The powder XRD pattern of the solvent-extracted sample depicted in Fig. 1 shows the occurrence of a clear reflection peak at the 1.5°(2) value. Referring to literatures [3,4], the single peak patterns of this type of material indicated the presence of uniform diameter pores in the mesoporous range where either the pore architecture of the materials is non-symmetrical or the particle sizes are small. Nitrogen adsorption–desorption isotherms of before (Fig. 2B) and after (Fig. 2A) template removing are showed in Fig. 2. The Fig. 2A displays a combination of several types of isotherms. At low relative pressure (P/P0 < 0.1), the high adsorbed quantity indicated the presence of considerate micropores in the material. At P/ P0 = 0.4–0.5, a hysteresis loop and obvious adsorption and desorption can be observed which indicate the presence of a mesoporous framework. The uptake at P/P0 > 0.8–0.9, which is already shown before template removing (Fig. 2B, SBET is about 32 m2/g), corresponds to the adsorption of inter-particles space, and the space is irregular in the size and shape and results in a broader pore size distribution of the material. This results in the significant slope even in its parts approaching the plateau in the isotherm. Generally, for the prepared worm-like uniformed material, BET surface area is about 669.3 ± 50 m2/g, pore volume is about 1.1 cm3/g. As depicted in Fig. 3, according to BJH pore size distribution analysis, the uniform worm-like pore size is about 3.6 nm. The representative TEM images for solvent-extracted samples are shown in Fig. 4. Notice the mesoporous silica is non-symmetrical worm-like morphology.

0.6

Relative pressure (P/P0)

10

2θ(Degree)

volume adsorpted cm3/g

0

0.2

0.06 0.04 0.02 0.00 2

4

6

8

10

12

14

16

18

20

Pore Size(nm) Fig. 3. BJH pore size distribution.

In the experiment, we found the pH and the ratio of TEOS/DODAC greatly effect the structure of the material. Only when the pH is around 12, the ratio of TEOS/DODAC is about 0.03–0.06 as well as TEOS slow adding, an ordered and uniform material can be obtained.

44

Y.-X. Zhao et al. / Microporous and Mesoporous Materials 124 (2009) 42–44

Fig. 4. High-resolution transmission electron micrographs of several samples.

During the synthesis course, before the white precipitate appeared, the system underwent a turbidity and subsequent flocculation, an analogous behavior that had been reported by J.H. Fendler et al. [8] when electrolyte was added to the single-compartment vesicles aqueous solution. The increased turbidity corresponds to osmotic shrinkage of the vesicles, upon the addition of electrolytes. It can be presumed that the DODAC/TEOS system undergoes a series reassembly process, from single-compartment vesicle to worm-like assembly. And this process is very sensitive to pH, TEOS/DODAC/H2O ratio and the TEOS adding speed. So the conditions to obtained uniformed worm-like material are some extent limited. 4. Conclusion Double-chained cationic surfactant DODAC is used successfully as structure-directing agent to synthesize mesoporous silica materials. The obtained material has non-symmetrical wormhole-like morphology, narrow distribution of pore size, larger volume of pores indicating DODAC is a suitable template for preparation of mesoporous materials.

Acknowledgments We acknowledge financial support from National Natural Science Foundation of China (20573071) and, Natural Science Foundation of Shanxi Province (20041017). We thank Research Institute of Daily Chemical Industry (RIDCI, Taiyuan Shanxi) for providing DODAC. References [1] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992) 710. [2] [a] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky, Science 279 (1998) 548; [b] D. Zhao, Q. Hou, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [3] P.T. Tanev, T.J. Pinnavaia, Science 267 (1995) 865. [4] S.A. Bagshaw, E. Prouzet, T.J. Pinnavaia, Science 269 (1995) 1242. [5] M. Jung, D.H. Hubert, P.H.H. Bomans, P.M. Frederik, J. Meuldijk, A.M. van Herk, H. Fischer, A.L. German, Langmuir 13 (1997) 6877–6880. [6] D.H.W. Hubert, M. Jung, P.M. Frederik, P.H.H. Bomans, J. Meuldijk, A.L. German, Adv. Mater. 12 (17) (2000) 1268–1290. [7] J. Hotz, W. Meier, Langmuir 14 (1998) 1031–1036. [8] C.D. Tran, P.L. Klahn Alejandro Romero, J.H. Fendler, J. Am. Chem. Soc. 100 (5) (1978) 1622–1623.